A class of machines exists in the art generally known as “scroll” machines for the displacement of various types of fluids. Such machines may be configured as an expander, a displacement engine, a pump, a compressor, etc., and the features of the present teachings are applicable to any one of these machines. For purposes of illustration, however, the disclosed embodiments are in the form of a hermetic refrigerant compressor.
Generally speaking, a scroll machine comprises two spiral scroll wraps of similar configuration, each mounted on a separate end plate to define a scroll member. The two scroll members are interfitted together with one of the scroll wraps being rotationally displaced 180° from the other. The machine operates by orbiting one scroll member (the “orbiting scroll”) with respect to the other scroll member (the “fixed scroll” or “non-orbiting scroll”) to make moving line contacts between the flanks of the respective wraps, defining moving isolated crescent-shaped pockets of fluid. The spirals are commonly formed as involutes of a circle, and ideally there is no relative rotation between the scroll members during operation; i.e., the motion is purely curvilinear translation (i.e., no rotation of any line in the body). The fluid pockets carry the fluid to be handled from a first zone in the scroll machine where a fluid inlet is provided, to a second zone in the machine where a fluid outlet is provided. The volume of a sealed pocket changes as it moves from the first zone to the second zone. At any one instant in time there will be at least one pair of sealed pockets; and where there are several pairs of sealed pockets at one time, each pair will have different volumes. In a compressor, the second zone is at a higher pressure than the first zone and is physically located centrally in the machine, the first zone being located at the outer periphery of the machine.
Two types of contacts define the fluid pockets formed between the scroll members, axially extending tangential line contacts between the spiral faces or flanks of the wraps caused by radial forces (“flank sealing”), and area contacts caused by axial forces between the plane edge surfaces (the “tips”) of each wrap and the opposite end plate (“tip sealing”). For high efficiency, good sealing must be achieved for both types of contacts; however, the present teachings are primarily concerned with tip sealing.
The concept of a scroll-type machine has thus been known for some time and has been recognized as having distinct advantages. For example, scroll machines have high isentropic and volumetric efficiency, and, hence, are relatively small and lightweight for a given capacity. They are quieter and more vibration free than many machines because they do not use large reciprocating parts (e.g., pistons, connecting rods, etc.); and because all fluid flow is in one direction with simultaneous compression in plural opposed pockets, there are less pressure-created vibrations. Such machines also tend to have high reliability and durability because of the relatively few moving parts utilized, the relatively low velocity of movement between the scrolls. Scroll machines which have compliance to allow tip leakage have an inherent forgiveness to fluid contamination.
One of the difficult areas of design in a scroll-type machine concerns the technique used to achieve tip sealing under all operating conditions, and also speeds in a variable speed machine. Conventionally, this has been accomplished by (1) using extremely accurate and very expensive machining techniques, (2) providing the wrap tips with spiral tip seals, which, unfortunately, are hard to assemble and often unreliable, or (3) applying an axially restoring force by axial biasing the orbiting scroll or the non-orbiting scroll towards the opposing scroll using compressed working fluid. The latter technique has some advantages but also presents problems, namely, in addition to providing a restoring force to balance the axial separating force, it is also necessary to balance the tipping moment on the scroll member due to pressure-generated radial forces which are dependent on suction and discharge pressures, as well as the inertial loads resulting from the orbital motion which is speed dependent. Thus, the axial balancing force must be relatively high, and will be optimal at only certain pressure and speed combinations.
The utilization of an axial restoring force requires one of the two scroll members to be mounted for axial movement with respect to the other scroll member. This can be accomplished by securing the non-orbiting scroll member to a main bearing housing by means of a plurality of bolts and a plurality of sleeve guides as disclosed in Assignee's U.S. Pat. No. 5,407,335, the disclosure of which is hereby incorporated herein by reference. In the mounting system which utilizes bolts and sleeve guides, arms formed on the non-orbiting scroll member are made to react against the sleeve guides. The sleeve guides hold the scroll member in proper alignment. The non-orbiting scroll member experiences gas forces in the radial and tangential direction whose centroid of application is at or near the mid-height of the scroll vane or wrap. The non-orbiting scroll member also experiences tip and base friction which can be randomly more on one than the other, but can be assumed as being equal and, therefore, having a centroid at or near the mid-height of the scroll wrap or vane. The non-orbiting scroll member additionally experiences flank contact forces from the centripetal acceleration of the orbiting scroll member which acts closer to the vane tip than at the base of the vane. All of these forces combine to yield a centroid of action which is located at a point just off the mid-height of the scroll wrap or vane toward the vane tip.
When the arms of the non-orbiting scroll member are located at the same elevation as the centroid of action of the forces experienced, the sleeve guides reaction could be equal and coplanar. When the arms are located near the tip of the vane of the non-orbiting scroll member, the reaction is not located at the centroid of action of the forces, it is offset from the centroid in a first direction. This offset produces a moment which reacts between the arm of the non-orbiting scroll member and the sleeve guide. Similarly, when the arms are located near the end plate of the non-orbiting scroll member, the reaction is again not located at the centroid of action of the forces, it is offset from the centroid in a second direction, opposite to the first direction. This offset also produces a moment which reacts between the arm of the non-orbiting scroll member and the sleeve guide.
Countering this moment is a moment produced by the hold-down force on the top of the non-orbiting scroll member, the axial gas separating force and the tip force pushing up on the vanes. The tip force can move to the radially outward most tip establishing a moment arm back to the centerline axis of the scroll wrap profile. The desire for high efficiency leads to a design with minimal tip load and, thus, the countering moment is of limited magnitude with no motivation to increase it.
In some scroll member designs, the sleeve guide reaction is so close to the non-orbiting scroll tip or so close to the non-orbiting end plate that it is far out of the plane of the centroid of action of the forces; and this causes the overturning moment to exceed the restoring moment. This causes the non-orbiting scroll member to rock up on one side, separating the tips from the bases of the scroll members on that side. This separation causes leakage which reduces the capacity of the compressor and, to a lesser extent, increases power.
The load which is applied to this sleeve guide tends to lean the sleeve guide away from the load. As this occurs, the load does not distribute evenly over the axial height of the non-orbiting scroll member arm, but it concentrates in the area near or away from the tip of the non-orbiting scroll member vane, near the bottom or top of the hole in the arm. This tendency increases the moment arm of the overturning moment.
A stepped geometry for the sleeve guide prevents contact between the arm of the non-orbiting scroll member and the sleeve guide at specific locations by reducing the diameter of the sleeve guide at that specific location. This concept allows the centroid of the reaction forces on the sleeve guide against the arms of the non-orbiting scroll member to be relocated from its normal axial position to a more preferred axial position.
In a first embodiment, the centroid of reaction of the sleeve guide focuses the centroid toward the top of the hole in the arm of the non-orbiting scroll member. This reduces the moment arm of the overturning moment for these scroll designs. The sleeve guide has a reduced diameter at a specified distance below the top of the sleeve, this distance being less than the axial height of the arm of the non-orbiting scroll member.
In another embodiment, the reduced diameter is located only at the mid-section of the sleeve guide. The reduction in diameter does not extend to either end of the sleeve guide. This enables the sleeve guide to be symmetrical so that it can be assembled with either end up to produce the same effect.
In another embodiment, the hole in the arm of the non-orbiting scroll member is machined as a stepped hole with the larger portion of the stepped hole being located nearest the vane tip.
In another embodiment, the centroid of reaction of the sleeve guide focuses the centroid toward the bottom of the hole in the arm of the non-orbiting scroll member. This reduces the moment arm of the overturning moment for these scroll designs. The sleeve guide has a reduced diameter at a specified distance above the top of the sleeve, this distance being less than the axial height of the arm of the non-orbiting scroll member.
In another embodiment, the reduced diameter is located only at the opposing ends of the sleeve guide. The reduction in diameter does not extend to the middle of the sleeve guide. This enables the sleeve guide to be symmetrical so that it can be assembled with either end up to produce the same effect.
In another embodiment, the hole in the arm of the non-orbiting scroll member is machined as a stepped hole with the larger portion of the stepped hole being located away from the vane tip.
In another embodiment, a scroll compressor includes a compression mechanism contained within a shell and including a non-orbiting scroll supported for axial displacement relative the shell and including an end plate having a wrap extending therefrom and a flange having a bore extending therethrough. A guide member may be axially fixed relative the shell and extend through the bore in the flange so that a first portion of the guide member is disposed within and generally abuts a first circumferential portion of the bore and a second portion of the guide member is disposed within and generally spaced apart from a second circumferential portion of the bore.
In another embodiment, a scroll compressor includes a compression mechanism contained within a shell and including a non-orbiting scroll supported for axial displacement relative the shell. The non-orbiting scroll includes an end plate having a wrap extending therefrom and a flange having a bore extending therethrough. A guide member is axially fixed relative the shell and extending through the bore in the flange. A first portion of the guide member is disposed within a circumferential portion of the bore and includes a first maximum width portion having a first width generally abutting the circumferential portion of the bore. A second portion of the guide member is disposed within the circumferential portion of the bore and includes a second maximum width portion having a second width generally less than the first width.
In another embodiment, a scroll compressor includes a compression mechanism contained within the shell and including a non-orbiting scroll supported for axial displacement relative the shell. The non-orbiting scroll includes an end plate having a wrap extending therefrom and a flange having a bore extending therethrough. A guide member is axially fixed relative the shell and extends through the bore in the flange. A first portion of the guide member is disposed within the bore, which includes first and second circumferential portions spaced axially apart from one another. The first circumferential portion generally abuts the guide member first portion at a first minimum width portion having a first width. The second circumferential portion includes a second minimum width portion having a second width generally greater than the first width, wherein the second circumferential portion is spaced radially apart from said guide member first portion to define a recess therebetween.
Further areas of applicability of the present teachings will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the claims.